A projector apparatus of today uses digital light processing technology to process the light beams from the light source to become image light beams for being projected onto the wall screen. Therefore, today's projector apparatus serves an integral part of a home theater system.
Note that the digital light processing technology is capable of modulating electrical signals into image light beams which are later projected successively or intermittently onto the large screen via a projection lens unit. A semiconductor chip (generally known as a DMD: digital micromirror device) is used in the projector apparatus, and includes several millions of tiny mirrors.
Referring to FIG. 1, a conventional projector apparatus 10 (generally known as DLP projector) using digital light processing technology is shown and includes a light source 12, a DMD chip 14 and a projection lens unit 16. The light source 12 is capable of producing light beams for the DMD chip 14 to modulate and reflect the light beams into image light beams for being projected onto a wall screen (not shown) via the projection lens unit 16. The projection lens unit 16 may include several optical lenses which magnify and project the magnified image onto the wall screen.
The light source 12 includes a lamp 121, a color-filtering wheel 122, a light integrator 123, a condensing lens unit 124, a reflective mirror 125 and a total internal reflection prism 126. A light-collecting shield is disposed around the lamp 121 in order to collect and focus the light beams. The color-filtering wheel 122 is disposed frontward of the lamp 121 in order to provide multi-colors effect. The light integrator 123 directs the light beams homogeneously into the condensing lens unit 124 which defines a light path for the light beams. Later, the reflective mirror 125 directs the light beams into the reflection prism 126, which, in turn, directs the light beams into the DMD chip 14 with a predetermined angle of incidence (generally 24 degrees) so that the DMD chip 14 when at the “On” status modulates and reflects the light beams into the projection lens unit 16. Finally, the projection lens unit 16 magnifies, focuses and projects the image onto the wall screen.
Referring again to FIG. 1, in the aforesaid conventional projector apparatus, the projection lens unit 16 is disposed parallel with the condensing lens unit 124 in order to reduce the dimension of the apparatus and the light beams emitted by the lamp 121 are directed perpendicularly to the reflection prism 126 with the assistance of the reflective mirror 125 such that the reflected light beams travel in a direction parallel with the light beams. Alternately, in other conventional projector apparatus, the condensing lens unit 124, the color-filtering wheel 122, and the projection lens unit 16 can be arranged in a straight line without employment of the reflective mirror 125.
In addition, there are still other conventional DLP projectors using three DMD chips, wherein each DMD chip is responsible for producing a specific color, such as blue, green and red.
The center core of the digital projector apparatus resides in the DMD chip 14 (see FIG. 2) that includes several millions of tiny mirrors 141. Each of the tiny mirrors is made from aluminum alloy, and has a cross-section of 14×14 micro millimeter that is smaller than cross-section of a single hair strand. As illustrated in FIG. 2A, each tiny mirror 141 is rotatable about the a-b axis and is generally rectangular in shape. FIG. 2B shows a cross-sectional view of the tiny mirror 141 taken along 8-8 lines in FIG. 2A, wherein the mirror 141 rotates 12 degrees in the anti-clockwise direction with respect to the axis a-b in case the tiny mirror 141 is at the “On” status, where the reflective light beam R1 of the incoming light beam Lo is directed to the projection lens unit 16 so as to project the image on the wall screen. On the other hand, the tiny mirror 141 rotates 12 degrees in the clockwise direction with respect to the axis a-b in case the former is at the “Off” status, where the reflective light beam R2 of the incoming light beam Lo is directed away from the projection lens unit 16. Since the digital information is referred to either “1” or “0”, the tiny mirror 141 rotates about the a-b axis in “On” and “Off” statuses.
Note that the tiny mirrors 141 in the DMD chip 14 rotate with respect to the axis a-b axis either in the clockwise or anti-clockwise direction when the digital signal is 0 or 1 according to the difference of the modulated voltages. When no modulated voltage is applied onto the chip 14, the tiny mirrors 141 extend in a direction parallel with a common plane defined by the chip 14. We generally call it a “Flat” status.
FIG. 3 illustrates how the projection lens unit 46 projects the projected image 26 onto the wall screen 24 by virtue of the reflected light beams R1 from the DMD chip 14. Note that the reflected light beams R1 from the incoming light beams Lo enter the projection lens unit 46 and are projected onto the wall screen 24 as a projected image when the tiny mirrors 141 are in the “On” status. On the other hand, the reflected light beams R2 from the incoming light beams Lo are directed away from the projection lens unit 46 when the tiny mirrors 141 are in the “Off” status so as to prevent undesired effect resulting on the projected image 26.
In fact, when the DMD chip 14 is in operation, several millions of the tiny mirrors 141 rotate reciprocally and ceaselessly in the clockwise and anti-clockwise directions (i.e. On>Flat>Off or Off>Flat>On). Under this condition, the reflected light beams generated during the converting period between the “On” and “Off” statuses, are generally known as “bias light beams”, and are not required for formation of the projected image. As a matter of fact, the bias light beams, which should not enter the projection lens unit 46, nevertheless enter the projection lens unit 46 during the converting period of the tiny mirrors 141 to cause the “ghost image” in the projected image 26. In other words, the “ghost image” is formed by the undesired internal reflection within the conventional DLP projector.
The conventional DLP projector is used in a conference room for presenting an intended scheme. Appearance of the “ghost image” during the presentation may lower the brightness and clarity of the projected image.
In case, the conventional DLP projector is used as part of a home theater system, the image projected onto the wall screen is required to be in better sharpness since the movie runs quickly. Under this condition, conversion of the tiny mirrors in the DMD chip between the “On” and “Off” statuses must also quicken in order to complement with the swift changing of the images. Appearance of the “ghost image” may lower the clarity and sharpness of the images being displayed, thereby degrading the display ability of the conventional DLP projector.